I would not expect decking to produce an airtight environment certainly if you have followed expansion gapping in the boards. The whole structure would benefit from air circulation and provision needs to made for air drying to remove damp and prevent mould. So a well designed deck should not prevent ventilation through air bricks. The most likely way an air brick could be blocked is if a joist is fixed to the wall along its length and passes over an air brick, however it is good practice to gap such a joist from the wall with suitable waterproof spacers.

Richard